A conventional magnetoresistive random access memory (hereafter, referred to as “MRAM”) in which a laminated ferri structure is used as the free layer of the tunnel magnetoresistive element (hereafter, referred to as “magnetoresistive element”) is disclosed in U.S. Pat. No. 6,545,906. This kind of MRAM is a so-called toggle MRAM. FIG. 1 is a sectional view showing a configuration of the conventional magnetoresistive element 125. The magnetoresistive element 125 is arranged between a write word line 126 and a write bit line 127 and separated away from both of them. The magnetoresistive element 125 includes a free layer 111, a tunnel insulating layer 112, a pinned layer 113 and an anti-ferromagnetic layer 114. The free layer 111 and the pinned layer 113 are formed with the tunnel insulating layer 112 being pinched between them. The pinned layer 113 is a laminated ferri structure in which a non-magnetic layer 117 is sandwiched between a ferromagnetic layer 116 and a ferromagnetic layer 118. The direction of the magnetization of the pinned layer 113 is fixed by the anti-ferromagnetic layer 114. The free layer 111 is also a laminated ferri structure in which a non-magnetic layer 120 is sandwiched between a ferromagnetic layer 119 and a ferromagnetic layer 121. Due to the laminated ferri structure, the magnetic field is not generated out of the pinned layer 113 and the free layer 111, unless an external magnetic field is applied.
FIG. 2 is a top view showing the configuration of the conventional magnetoresistive element 125. A plurality of write word lines 126 and a plurality of write bit lines 127 are arranged orthogonally to each other. However, only one write word line 126 and one write bit line 127 are shown in the drawing. The magnetoresistive element 125 is arranged at each of the intersections of the plurality of write word lines 126 and the plurality of write bit lines 127. The magnetoresistive element 125 is oriented to the direction in which an easily-magnetized direction (a magnetization easy axis: indicated by a broken line arrow mark in the magnetoresistive element 125) is inclined at 45 degrees with respect to both of the write word line 126 and the write bit line 127.
This MRAM is the toggle MRAM. In a case of a memory cell 120 in this toggle MRAM, writing is executed only in the manner [1]→[0] or [0]→[1]. [1] cannot be overwritten to [1], and [0] cannot be overwritten to [0]. In the overwriting operation, at first, a reading operation is performed on the memory cell 120 on which the writing is tried to be performed (hereafter, also referred to as “selected cell”).
Next, when the writing is executed, a write current IWBL is supplied to the write bit line 127. Next, after a time interval, a write current IWWL is supplied to the word line 126.
FIG. 3A to FIG. 3C are graphs showing the trajectories of the writing magnetic field induced by the write current. FIG. 3A shows the case of the selected cell (the memory cell 120 selected by the selected write bit line 127 and the selected write word line 126). FIG. 3B shows the case of the non-selected cell (the memory cell 120 connected to either one of the selected write bit line 127 and the selected write word line 126). As shown in FIG. 3A, when this trajectory goes round a flop magnetic field Hf, the magnetization of the free layer 111 is changed, such as [1]→[0] or [0]→[1]. On the other hand, as shown in FIG. 3B, when this trajectory does not go round the flop magnetic field Hf, the magnetization of the free layer 111 is not changed.
A magnetization inversion mode, which is referred to as the direct mode, exists in the neighborhood of the flop magnetic field, as described in U.S. Pat. No. 6,545,906, which can be used for the MRAM. In this direct mode, it is a merit that a method of the magnetization of a magnetic body can be determined in accordance with the data to be written on the memory cell 120. That is, when [1] is to be written, the process for writing [1] is carried out, irrespectively of the storage state of the memory cell 120 immediately before. FIG. 3C shows a case of a selected cell in the direct mode. As shown in FIG. 3C, when this trajectory exceeds the flop magnetic field Hf, the magnetization of the free layer 111 becomes, for example, [1] or [0]→[1]. However, when a giant magnetic field is applied, the magnetization of the laminated ferri structure is saturated, and the magnetizations of the two ferromagnetic bodies 116, 118 in the free layer 111 become approximately same direction as shown in FIG. 4. That is, the direction of the magnetization of the ferromagnetic layer 116 and the direction of the magnetization of the ferromagnetic layer 118 become unstable, which brings about disturbances in data.
On the other hand, there is a case that a magnet exists around a system (exemplified by the personal computer) using the MRAM. For example, a magnet is used in the speaker and the like. The possibility that a magnet stays near the MRAM cannot be perfectly removed. When an external magnetic field is applied to the MRAM, the following problems occur. For example, when an external magnetic field is applied during the writing operation, the possibility of erroneous writing becomes high. FIGS. 5A to 5C are graphs showing the trajectory of the writing magnetic field induced by the write current when an external magnetic field is applied. FIG. 5A shows the case of the selected cell, FIG. 5B shows the case of the non-selected cell, and FIG. 5C shows the holding cell (a memory cell 120 that is not connected to any of the selected write bit line 127 and the selected write word line 126), respectively.
With reference to FIG. 5A, there is a possibility that the trajectory of the magnetic field of a selected cell does not pass outside the flop magnetic field Hf, because the trajectory is shifted by an external magnetic field HD. That is, there is a risk of the failure in the writing. With reference to FIG. 5B, there is a possibility that the trajectory of the magnetic field of the non-selected cell is shifted by the external magnetic field HD and approaches the neighborhood of the flop magnetic field Hf. That is, there is a risk that the writing (magnetization inversion) through the direct mode occurs in the non-selected cell. With reference to FIG. 5C, when the external magnetic field HD near the flop magnetic field Hf is applied to a holding cell, there is a risk of the occurrence of the writing (magnetization inversion) through the direct mode. That is, the application of an external magnetic field brings about the problem of the drop in the reliability, such as the case that the writing is not performed correctly or stored data is broken. Thus, a technique for protecting data of the MRAM from external magnetic fields and avoiding the erroneous operations is desired.
As a method for protecting data from an external magnetic field, a technique in which a soft-magnetic body is arranged around the MRAM or a system using the MRAM so that a magnetic flux flows through the shielding plate of the soft-magnetic body is known. For example, in Japanese Laid Open Patent Application JP-P2004-207322A, a magnetic memory device is disclosed. This magnetic memory device is a magnetic random access memory composed of memory elements, each of which is laminated with: a magnetization pinned layer whose magnetization direction is fixed; and a magnetic layer whose magnetization direction is changeable are laminated.
The plurality of memory elements, or the memory element and the other element are laminated, and a magnetic shielding layer is formed at least on an area occupied by the memory elements for magnetically shielding the memory elements. FIG. 6 is a sectional view showing the MRAM (Magnetic Memory Device) to which this conventional data protecting method is applied. That is, the MRAM contains: a package 131, which includes therein a filler 132, an MRAM chip 134, a bonding wire 135 and a lead frame 136; and shielding plates (magnetic shielding layers) 133 made of soft magnetic materials formed over and under the package 131 with the MRAM chip 134 between.
As a related technique, in Japanese Laid Open Patent Application JP-P 2003-115578A, a nonvolatile solid magnetic memory device, a manufacturing method and a multi-chip package thereof are disclosed. This nonvolatile solid magnetic memory device has an MRAM chip and a package placed around the MRAM chip. The MRAM chip is composed of: magnetoresistive elements arranged in a matrix on a substrate; bit lines connected to the magnetoresistive elements; write lines to apply a magnetic field to the magnetoresistive elements; and field effect transistors, and has a plurality of memory elements. A magnetic shielding structure for shielding the MRAM chip from an external scattered magnetic field is formed.
In Japanese Laid Open Patent Application JP-P 2004-186658A, a magnetic detecting element and a manufacturing method thereof are disclosed. This magnetic detecting element has: a multi-layer film in which at least a first anti-ferromagnetic layer, a pinned magnetic layer, a non-magnetic material layer and a free magnetic layer are laminated on a substrate; and a magnetization control layer for controlling the magnetization of the free magnetic layer. The pinned magnetic layer has: a first magnetic layer extending in a track width direction and is located on the side in contact with the first anti-ferromagnetic layer; a second magnetic layer opposite to the first magnetic layer in the direction of the film; and a non-magnetic intermediate layer located between the first and second magnetic layer. The magnetization of the first magnetic layer and that of the second magnetic layer are anti-parallel to each other. The first anti-ferromagnetic layer is formed in contact with, from the film thickness direction, both side ends in the track width direction of the first magnetic layer, through a gap of a predetermined interval in the track width direction. The characteristic is that the electric resistances are changed based on the magnetization direction of the free magnetic layer in the gap and the magnetization direction inside the second magnetic layer.
In Japanese Laid Open Patent Application JP-P 2004-221288A, a magnetic memory device is disclosed. This magnetic memory device is a magnetic random access memory constituted by memory elements, each of which is composed of: a magnetization pinned layer whose magnetization direction is fixed; and a magnetic layer whose magnetization direction is changeable are laminated. A magnetic shielding layer for magnetically shielding the memory elements is formed. This magnetic memory device is characterized in that the memory elements are located while avoiding the periphery and center of the magnetic shielding layer.
In Japanese Laid Open Patent Application JP-P 2005-94002A, a magnetic memory cell, a magnetic memory array and a manufacturing method thereof are disclosed. This magnetic memory cell contains a basic body, a magnetic tunnel junction element, a first insulating layer, a magnetic shielding layer and a second insulating layer. The magnetic tunnel junction element is formed in a partial region on the basic body. The first insulating layer is formed to cover the regions except the partial region on the basic body and cover the all edge surface of the magnetic tunnel junction element.
The magnetic shielding layer is formed to surround at least a part of the periphery of the magnetic tunnel junction element through the first insulating layer and is electrically insulated from the basic body and the magnetic tunnel junction element. The second insulating layer is formed to cover the portions except the magnetic tunnel junction element. This is characterized in that the magnetic tunnel junction element and the magnetism shielding layer are magneto-statically coupled to each other.
In Japanese Laid Open Patent Application JP-P2005-158985A, a mounting structure and a mounting substrate of a magnetic memory device are disclosed. In the mounting structure of this magnetic layer device, the magnetism shielding layer for magnetically shielding the magnetic random access memory constituted by a memory element, in which the magnetization pinned layer whose magnetization direction is fixed and the magnetic layer whose magnetization direction is changeable are laminated, is formed on a printed wiring board for mounting and/or an interposer substrate.